Intercarrier sound detecting apparatus for a television receiver

Abstract

An intercarrier sound detecting apparatus for a television receiver includes an antenna for receiving a television signal; a tuner for selecting a desired frequency range of the received television signal from the antenna and producing a tuned signal having a video intermediate frequency component in response thereto; a filter for extracting the video intermediate frequency component from the tuned signal; video intermediate frequency amplifiers for producing a video intermediate frequency signal having an amplitude-modulated video carrier component, in response to the extracted video intermediate frequency component; a phase-locked loop which phase-locks the video intermediate frequency signal with respect to the amplitude-modulated video carrier component thereof and produces an output signal having a 4.5 MHz beat signal component in response thereto; a band pass filter for transmitting substantially only the 4.5 MHz beat signal component; and a frequency discriminator for producing a sound signal in response to the 4.5 MHz beat signal component transmitted through the band pass filter.

What is claimed is: 
     
       1. Sound detecting apparatus for a television receiver comprising: receiving means for receiving a television signal including an amplitude-modulated video carrier component and a sound carrier component;   video intermediate frequency means for producing a video intermediate frequency signal having said amplitude-modulated video carrier component and said sound carrier component, in response to said received television signal;   phase-locked loop means for phase-locking said video intermediate frequency signal with respect to said amplitude-modulated video carrier component thereof and producing an output signal in response thereto; and   sound signal generating means for producing a sound signal in response to said output signal.   
     
     
       2. Sound detecting apparatus according to claim 1; in which said phase-locked loop means includes phase comparator means for producing said output signal in response to said video intermediate frequency signal and a voltage controlled oscillation signal, control means for producing a control signal in response to said output signal, and voltage controlled oscillator means for producing said voltage controlled oscillation signal in response to said control signal. 
     
     
       3. Sound detecting apparatus according to claim 2; in which said control means includes low pass filter means for producing said control signal. 
     
     
       4. Sound detecting apparatus according to claim 3; in which said low pass filter means includes a low pass filter having a cut-off frequency lower than 31.5 KHz. 
     
     
       5. Sound detecting apparatus according to claim 2; in which said control means includes DC amplifier means supplied with said output signal to produce a DC amplified signal and low pass filter means for producing said control signal in response to said DC amplified signal. 
     
     
       6. Sound detecting apparatus according to claim 1; in which said output signal from said phase-locked loop means includes a 4.5 MHz beat signal component; and said sound signal generating means includes band pass filter means for transmitting substantially only the 4.5 MHz beat signal component, and frequency discriminator means for producing said sound signal in response to said 4.5 MHz beat signal component transmitted through said band pass filter means. 
     
     
       7. Sound detecting apparatus according to claim 6; which said sound signal generating means further includes amplifier means for amplifying said 4.5 MHz beat signal component transmitted through said band pass filter means, limiter means for amplitude limiting said 4.5 MHz beat signal component amplified by said amplifier means to produce a 4.5 MHz amplitude limited signal, and said frequency discriminator means frequency discriminates said 4.5 MHz amplitude limited signal to produce said sound signal. 
     
     
       8. Sound detecting apparatus according to claim 1; in which said receiving means and said video intermediate frequency means include antenna means for receiving said television signal, tuner means for selecting a desired frequency range of said received television signal from said antenna means and producing a tuned signal having said video intermediate frequency components in response thereto, filter means for extracting said video intermediate frequency components from said tuned signal, and video intermediate frequency amplifier means for producing said video intermediate frequency signal in response to said extracted video intermediate frequency components.